Various kinds of axle units have heretofore been used, in which an outer ring and an inner ring are rotatably combined via rolling members in order to rotatably support a wheel on a suspension unit. It is necessary for the axle unit used for supporting the driven wheel on the independent suspension and rotatably driving the driven wheel, to smoothly transmit the rotation of the drive shaft to the wheel (while ensuring constant velocity), in combination with a constant velocity joint, regardless of relative displacement between the differential gear and the driven wheel and the steering angle imparted to the wheel. The axle unit for driving the vehicle wheel, which is a so-called fourth generation hub unit, can be combined with such a constant velocity joint and can be constructed relatively compact and lightweight. Such an axle unit has heretofore been disclosed in Japanese Patent Publication Tokukai Hei No. 7-317754, or in U.S. Pat. No. 5,674,011.
FIG. 36 shows one example of a conventional construction disclosed in Japanese Patent Publication Tokukai Hei No. 7-317754. An outer ring 1 which does not rotate while being supported on the suspension unit when incorporated into the vehicle, has an outward flange shaped attachment portion 2 for supporting the outer ring on the suspension unit, on the outer peripheral face thereof, and two rows of outer ring raceways 3 on the inner peripheral face thereof.
On the radially inner side of the outer ring 1, a hub 6 formed by combining a first element 4 and a second element 5 is disposed. Of these, the first element 4 is formed in a cylindrical form having an mount flange 7 for supporting the wheel on one end side (on the left end side in FIG. 36), and an inner ring raceway 8 on the other end side (on the right end side in FIG. 36). The second element 5 has on one end side (the left end side in FIG. 36) a cylindrical portion 9 for externally securing the first element 4, and on the other end side (the right end side in FIG. 36) a housing 11 which is the outer ring of a constant velocity joint 10 of a Rzeppa type, with the inner ring raceway 8 arranged on the outer peripheral face of the middle part thereof.
By disposing a plurality of rolling members 12, respectively between the outer ring raceways 3 and the inner ring raceways 8, the hub 6 is rotatably supported on the inside of the outer ring 1.
In a position where the inner peripheral face of the first element 4 and the outer peripheral face of the second element 5 are joined in an aligned manner, an outside engagement groove 13 and an inside engagement groove 14 are respectively formed, and a stop ring 15 is provided between and engaged into these engagement grooves 13, 14, thereby preventing that the first element 1 from coming away from the second element 5.
Moreover, a weld 17 is applied between an outer peripheral rim portion on one end face (the left end face in FIG. 36) of the second element 5 and an inner peripheral rim portion of a stepped portion 16 formed on the inner peripheral face of the first element 4, to securely connect the first and second elements 4 and 5 to each other.
Furthermore, substantially cylindrical covers 18 made of metal such as stainless steel plate, and circular seal rings 19 made of a resilient material such as rubber or elastomer are provided between the opening portions at opposite ends of the outer ring I and the outer peripheral face in the middle part of the hub 6. On the inside of the middle part of the second element 5, an isolating member 20 for closing off the inside of the second element 5 is provided. These covers 18, seal rings 19 and isolating member 20 shut off the portion where the plurality of rolling members 12 are installed, or the portion of constant velocity joint 10, from outside, and prevent grease existing inside the portion from leaking to the outside as well as preventing the ingress of foreign matter such as rainwater, dust or the like.
The constant velocity joint 10 comprises the housing 11, an inner ring 21, a retainer 22 and a plurality of balls 23. The inner ring 21 is fixed to a tip end of a drive shaft (not shown) which is rotatably driven via a transmission by an engine. On the outer peripheral face of this inner ring 21, there are respectively formed in a direction at right angles to the circumferential direction, six inner engagement grooves 24 having a section of an arc when cut on a virtual plane orthogonal to the central axis of the inner ring 21, at even spacing in the circumferential direction.
At a position opposite to the inner engagement grooves 24 on the inner peripheral face of the housing 11, there are similarly formed respectively in a direction at right angles to the circumferential direction, six outer engagement grooves 25 having a section of an arc.
The retainer 22 is formed in an overall annular shape, having a section of an arc, and is held between the outer peripheral face of the inner ring 21 and the inner peripheral face of the housing 11. Pockets 26 are respectively formed in the retainer 22 at the six positions in the circumferential direction thereof, being positions aligned with the inside and outside engagement grooves 24 and 25, and the above-mentioned balls (six in total) are retained therein, one inside each of the pockets 26. These balls 23 can be freely rolled along the inside and outside engagement grooves 24 and 25, while being retained in each pocket 26, respectively.
When the axle unit for driving the vehicle wheel constructed as described above is fitted to a vehicle, the outer ring 1 is supported on the suspension unit by the attachment portion 2, and the driven wheel is fixed to the first element 4 by the mount flange 7.
The drive shaft (not shown) is rotatably driven via the transmission by the engine, and the tip portion of the drive shaft is spline-engaged to the inside of the inner ring 21 of the constant velocity joint 10. At the time of driving an automobile, the rotation of the inner ring 21 is transmitted to the hub 6 including the second element 5 via the plurality of balls 23 to rotatably drive the driven wheel.
FIG. 37 shows a second example of a conventional construction which is disclosed in the abovementioned U.S. Pat. No. 5,674,011. In the case of the second example of conventional construction, two rows of outer ring raceways 3 are disposed on the inner peripheral face of the outer ring 1 which does not rotate at the time of use, being internally fixed to a knuckle 40 of a suspension unit.
A mount flange 7 for supporting the wheel, is disposed on one end side (on the left end side in FIG. 37) of the outer peripheral face of the hub 6a, and two rows of inner ring raceways 8 are disposed on the other end side (on the right end side in FIG, 37) via a pair of inner rings 50. The inner rings 50 are supported and secured to the body of the hub 6a by means of a crimped portion 27 formed by bending the other end of the hub 6a radially outward.
A plurality of rolling members 12 are respectively disposed between the outer ring raceways 3 and the inner ring raceways 8 to rotatably support the hub 6a inside of the outer ring 1.
A splined bore 28 is provided in the central portion of the hub 6a. The hub 6a and a drive shaft member 29 are thus combined to form an axle unit for driving a vehicle wheel. On one end side of the drive shaft member 29, there is provided a splined shaft 30 engaging with the splined bore 28. In addition, on the other end side of the drive shaft member 29 is a housing 11 which is the outer ring of the constant velocity joint. The drive shaft member 29 and the hub 6a are combined together such that the splined shaft 30 is inserted into the splined bore 28, and a coupling member 31 made of a resilient material is interlockingly engaged with the members 29 and 6a to thereby prevent separation. The coupling member 31 is provided with encoders 32 made of a magnetic material or a permanent magnet to make it possible to detect the rotation speed of the two members 29 and 6a.
FIG. 38 shows a third example of a conventional construction which is disclosed in Japanese Utility Model Registration No. 2,573,325. In the case of the third example of conventional construction, a hub 6b is spline-engaged with a portion of an end of an axle 92 exposed from the end of an axle pipe 93. The hub 6b is rotatably supported by rolling members arranged in two rows inside of a fixed outer ring 1a.
In addition, a stop ring 15a in the form of a segment circle is engaged in an engagement groove 94 formed in the tip portion of the axle 92 at a portion projecting from the spline engagement with the hub 6b, to prevent the hub 6b from coming out from the axle 92.
FIG. 39 shows a fourth example of a conventional construction which is disclosed in U.S. Pat. No. 4,881,842. In the case of the fourth example of conventional construction, a hub 6c is rotatably supported by two rows of rolling members inside of an outer ring 1b fixed to a knuckle 40.
A splined shaft 30 is spline-engaged with a splined bore 28 formed in the central portion of the hub 6c. In addition, a housing 11 which is the outer ring of the constant velocity joint is disposed on the base end (the right end in FIG. 39) of the splined shaft 30. On the tip end face (the left end face in FIG. 39) of the splined shaft 30, is formed an attachment portion 95 for engaging with a tool for pulling the splined shaft 30 into the splined bore 28.
The hub 6c is prevented from coming out from the splined shaft 30 by a stop ring 15b fitted in the engagement groove formed in a portion on the tip end side on the outer peripheral face of the splined shaft 30. In this condition, a resilient ring 96 is resiliently compressed between the hub 6c and the housing 11 to prevent play of the hub 6c on the splined shaft 30.
FIG. 40 shows a fifth example of a conventional construction which is disclosed in U.S. Pat. No. 5,492,417. In the case of the fifth example of conventional construction, a hub 6d is rotatably supported by two rows of rolling members inside of an outer ring 1c fixed to a knuckle 40. An inner ring 50 externally fitted to the hub 6d is prevented from moving axially, with a stop ring 97 fitted in the hub 6d.
In addition, the tip portion of a sleeve 98 (the left end in FIG. 40) of a constant velocity joint, which is spline-engaged with the axially inner end (the right end in FIG. 40) of the hub 6d covers the stop ring 97 to prevent the stop ring 97 from coming off from the hub 6d.
A stop ring 15c is positioned between and engaged with the outer peripheral face of the inner end of the hub 6d and the inner peripheral face of the sleeve 98 to prevent the hub 6d from coming out from the sleeve 98. A gear-like undulation portion 99 is formed on the outer peripheral face of the tip portion of the sleeve 98 so that this portion functions as an encoder. A rotation speed detection sensor 101 supported on the outer ring 1c via a seal ring 100 faces the undulation portion 99 so as to detect the rotation speed of the sleeve 98 and the hub 6d.
In the case of the first example of the conventional construction shown in FIG. 36, transmission of the rotation force between the first element 4 and the second element 5 which constitute the hub 6 must be effected by the portion of weld 17. That is to say, it is necessary to transmit a large torque for driving, between the first element 4 for supporting the wheel and the second element 5 coupled to the drive shaft.
However, since these elements 4 and 5 are engaged with each other at their cylindrical faces, a large torque cannot be transmitted at the engaging faces. It is therefore required to transmit the large torque through the portion of weld 17. Hence the weld 17 needs to be a full peripheral built up weld in order to increase the strength of the portion of weld 17 sufficiently. When the weld 17 is a built up weld around the whole periphery however, the shape of the portion of inner ring raceway 8 formed on the outer peripheral face of the first element 4 may be distorted, or the hardness of the portion of inner ring raceway 8 may be decreased, due to the heat at the time of welding. Hence the durability of the rolling bearing unit including this inner ring raceways 8 cannot be sufficiently ensured.
In the case of the second example of the conventional construction shown in FIG. 37, since the separation between the hub 6a and the drive shaft member 29 is prevented by the coupling member 31 made of a resilient material, the function of preventing the separation is rather uncertain. That is to say, when an automobile turns abruptly, a large cornering force is applied to the hub 6a in the direction of pulling this hub 6a away from the drive shaft member 29, based on the large thrust load due to a centrifugal force applied to the hub 6a from the wheel. Therefore in the case of such a large force it is very difficult to reliably prevent the separation of the hub 6a from the drive shaft member 29, by means of the coupling member 31. Hence sufficient reliability cannot be ensured.
The third example of the conventional construction shown in FIG. 38 relates to a so-called semi-floating type construction which is a non-independent suspension type suspension. In the case of such a construction, the splined engagement portion can be shut off from the outside space by the coupling portion of the axle pipe 93 and the outer ring 1a. Therefore, it is not necessary to provide a sealing device between the axle and the hub to shut off the splined engagement portion from the outside space. The third example of such a conventional construction has a quite different basic construction from that of the present invention in which the driven wheel supported by an independent type suspension is rotatably supported with respect to the suspension unit.
In the case of the fourth example of the conventional construction shown in FIG. 39, a member for shutting off the splined engagement portion from the outside is not provided. Therefore, the ingress of foreign matter such as rain water containing dust into the splined engagement portion cannot be avoided. Moreover, in the case of the construction as shown in FIG. 39, in which play of the hub 6c with respect to the splined shaft 30 is prevented by the resilient ring 96, and the resilient ring 96 can be deformed due to axial load causing sliding motion in the splined engagement portion, and then if foreign matter enters into the splined engagement portion, the splined engagement portion is worn, and the durability is deteriorated, which is unsatisfactory.
In the case of the fifth example of the conventional construction shown in FIG. 40, since the splined engagement portion is disposed in a portion protruding inward from the inner end opening of the outer ring 1c, the axial dimension of the whole axle unit for driving the vehicle wheel is increased, and a compact and lightweight structure cannot be realized.
The axle unit for driving the vehicle wheel according to the present invention has been developed in order to address the above-mentioned problems.